I have a Samsung R580 notebook in very good condition, when I test the
power supply I get very low (0.6V) voltage on the pin and also on the
inner barrel. (The plug has earth on the outer barrel and then a
separate line on the inner barrel and also a central pin, again
separate) I assume the pin is a sense pin that *may* only ramp the V
up when the unit is connected?

When I connect the adapter with the unit dismantled I get no voltage
across any of the pins on the DC IN plug.

Do you suppose this is a faulty power supply or is the fault with the
laptop?

I'm considering just using a separate 19v adapter but am uncertain as
to whether the V+ should be on the centre pin or the inner barrel.